Pneumothorax refers to the pathophysiological condition caused by the rupture of the dirty pleura without trauma or human factors, and the gas enters the pleural cavity resulting in pneumothorax. Pneumothorax is called idiopathic pneumothorax if it is formed by rupture of subpleural emphysema bubbles without obvious lung lesions; secondary pneumothorax is called secondary pneumothorax if it is secondary to chronic obstructive pulmonary emphysema, tuberculosis, pleural and pulmonary diseases. According to the pathophysiological changes, there are three types of pneumothorax: closed (simple), open (traffic) and tension (high-pressure). According to the presence or absence of primary disease, spontaneous pneumothorax can be divided into two types: primary and secondary pneumothorax. X-ray presentation is the examination of choice for diagnosing pneumothorax. It can show the degree of lung compression, lung condition, the presence of pleural adhesions, pleural effusion and mediastinal displacement, etc. The typical X-ray presentation of pneumothorax is: a thin line of convex arc-shaped shadow, with the compressed lung tissue inside the line and no lung texture outside the line, and a significant increase in translucency. If the pneumothorax extends to the lower part, the angle of the rib diaphragm shows sharp. The small amount of gas is often confined to the apical part of the lung and is often obscured by bone. When the patient is asked to exhale deeply, the atrophied lung shrinks even more and the density increases, showing a sharper contrast with the outer zone of gas accumulation translucency, thus showing the pneumothoracic zone. A restricted pneumothorax is easily missed during posterior-anterior X-ray examination, and it is necessary to rotate the position under X-ray fluoroscopy in order to see the pneumothorax. In massive pneumothorax, the lung is compressed and gathered in the hilar region in a round spherical shadow. If there are lesions or pleural adhesions in the lung, the shadow will be lobulated or irregular. Massive pneumothorax or tension pneumothorax shows the mediastinum and heart shifting to the healthy side. If the pneumothorax is combined with pleural effusion, there is a liquid-air surface, and the fluid surface can be seen to move with the change of position under fluoroscopy. If there is a translucent band around the cardiac border, mediastinal emphysema should be considered. The basic CT manifestation of pneumothorax is the appearance of extremely low-density gas shadow in the pleural cavity, accompanied by varying degrees of compression and atrophy of lung tissue. The diagnosis of pneumothorax containing very small amounts of gas and limited pneumothorax located mainly in the anterior and middle pleural cavities should generally be observed under the lung window conditions in the low window position, which can be missed on X-ray plain film without the disadvantage of image overlap on CT, making the diagnosis very easy. In patients with extensive subcutaneous emphysema, CT often reveals a pneumothorax that is negative on X-ray.